Musical instrument circuit



Jam 25, 1966 w. J. ANDERSON MUSICAL INSTRUMENT CIRCUT Filed MaIOh 7, 1961 3,231,653 MUSICAL INSTRUMENT CmCUIT Walter I. Anderson, Elgin, Ill., assigner to Chicago Musical Instrument Co., Lincolnwood, Ill., a corporation of Illinois Filed Mar. 7, 1961, Ser. No. 94,067 9 Claims. (Cl. SLi- 1.01)

This invention relates generally to musical instrument circuits, and more specifically to an improved switch circuit for an electronic organ type of musical instrument.

Although the principles of the present invention may be included in Various musical instruments, a particularly useful application is made in an electronic organ type of instrument, wherein savings in the number of components required, over prior circuits, is most dramatically apparent.

In particular, where a musical instrument includes a source of signal voltage which is of relatively high impedance, switch means incorporated between such source of signal and the conventional audio-amplifier must be suitably protected to prevent capacitative coupling between adjacent switch elements. Heretofore, it has been `customary to provide such protection by means of a grounding Contact which is close-circuited with the signal source whenever the key-operated switch is in a released or nonplaying position. This mode of protection thus requires a grounding contact for every playing Contact, together with suitable resistance means which are duplicated for each switch.

The instant invention employs an electronic switch between the signal source and the key-operated switch, which electronic switch is closed by the closing of the key-operated switch. It will be seen that by such structure, the individual key-operated switches are protected against unwanted coupling when in the open position, without the provision of separate grounding contacts for each switch, and without duplicating resistance means otherwise provided for each key-operated playing switch. Use of this invention with certain tyeps of chord keying devices enables such chord keying devices to ibe constructed more simply, and enables chord keying devices not otherwise usable with high impedance signal sources to be used therewith.

Accordingly, it is an object of the present invention to provide an improved switching circuit for a musical instrument. v A

A still further object of the present invention is to provide a circuit which precludes capacitative coupling between elements of key-operated switches.

A still further object of the present invention is to provide a circuit for a key-operated switch wherein there is substantially no voltage drop thereacross when it is in either the open or the closed position.

Yet another object of the present invention is to provide a switching circuit which has substantially no voltage drop across the elements of a key-operated switch Awhen in the open position, to prevent coupling therebeltween.

Yet another object of the present invention is to pro- /vide an electronic switch which has the signal source voltage applied to one side thereof and which has substantially no D.-C. voltage drop thereacross, both when it is open-circuited and when it is close-circuited.

A still further object of the present invention is to provide a switching circuit for an electronic organ wherein a large number of heretofore used components are elimiv nated.

United States Patent O 3,231,558 Patented Jan. 25,1966

switches, and wherein a minimum number of resistance elements are employed.

Many other advantages, features and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheet of drawings in which a preferred structural embodiment incorporating the principles the present invention is shown by way of illustrative example.

On the drawing:

The figure is a schematic diagram showing a representative portion of an electrical circuit for a musical instrument provided in accordance with the principles of the present invention.

As shown on the drawing:

The principles of this invention are particularly useful when embodied in an electrical musical instrument, the circuit of which is illustrated on the drawing, generally indicated by the numeral 10. The instrument circuit 10 includes a plurality of tone signal generators 11, each of which is a high impedance source of voltage, an electronic switch 12, a resistor 13 associated with each high impedance voltage source type oftone signal generator 11, a plurality of each of two types of parallel circuit paths 14, 15, a key-operated switch 16 in each of the paths 14, a key-operated switch 17 in each of the circuit paths 15, a number `of collectors or collector members 18, 19, a coupling capacitor 20 for each collector 18, 19, a tab switch 21 for each collector 18, 19, an A.C.signal responsive means 22 for the collectors 18, 19 jointly, a resistance path 23 to ground for each of the collectors 18, 19, and a supplemental or auxiliary optional source Vof D.C.-voltage for each of the electronic switches 12, in-

dicated by the resistors 24.

The high impedance source of voltage 11 has an A.C. component or A.C.signal, and a D.C.component or B+ signal which jointly appear at one terminal of the corresponding electronic switches 12. The structural details of the source are known in the art and may comprise, for example, the plate of an Eccles-Jordan circuit. Other known high impedance sources of voltage may be considered to be equivalent. In this invention, for a D.C. signal I relay upon the D.C.component normally present in such source of voltage, and to make the drawing hereof easier to follow, I have illustrated this inherent feature of such signal source as a B-lbus 25 coupled to each plate by a load resistor 26.

The electronic switch 12 may comprise a gas tube, or more specifically may comprise a cold cathode gas discharge tube as illustrated. The electronic switch 12 has a minimum conducting or ignition potential which is below the D.C.potential, below the combined A.CD.C. potential, and may be below the peak A.C.potential.

vThus, as later explained, voltage from the source 11 may be employed to ignite or otherwise render the electronic switch 12 conductive.

The electronic switch 12 and the resistor 13 associated with each source 11 are connected in series between such source 11 and a plurality of switches 16, or 17, or both. It will be noted that in each instance, the electronic switch 12 and the resistor 13 are common to all of the circuit paths 14, 15 which have connection with a particular source 11.

A plurality of parallel circuit paths 14 is provided for each of certain of the signal sources 11, a group of such parallel paths being provided for at least a twelve-note range within one octave. This type of circuit is particularly adapted to be employed in a switch assembly adapted to play chords wherein various combinations of three different switches 16 are simultaneously actuated by a single key or key button to provide a chord signal on the common collector 18. In accordance with this invention, it is possible to dispose the individual switches 16 of various notes in close mechanical proximity to each other, and without grounding out the movable element of open switches 16, without any capacitative coupling occurring between various elements of the various switches 16. It will also be noted that a single resistor 13 suices, not only for the switches 16, but also for the switches 17. It is to be understood that the instant invention may be employed to advantage with structure which employs the collector 18 or chord feature, with the structure associated with the other tabs omitted, and that the instant invention may be employed to advantage with structure wherein the chord switching circuitry is omitted, the latter being illustrated by the switches 17 associated with the note C5. Various combinations of octavely and otherwise related switches 17 are closed by the actuation of a single playing key, in a known manner, to provide the desired combination of harmonics on the various collector buses 19.

As illustrated by the note range C2-C5, the relatively movable conducting elements in each of the switches 16, 17 are ungrounded when each switch is in the open position.

It will be noted that the collector or collector member 18 is common to a plurality of key-operated switches 16 from any one source 11, and is also common to a plurality of switches 16 from a number of sources 11. The collectors 19 are each common to a number of switches 17 each associated with a separate source 11.

The designations given for the six lower tab switches 21 are intended to be representative, and it is apparent that the number of tab switches and associated circuits could be increased or decreased as required. The coupling capacitors for each tab circuit serve to block passage of direct current from the various switching circuits.

The A.C.signal responsive means 22 includes conventional voicing circuit means 27, a conventional audioamplifier 28, and a conventional speaker 29.

The resistance in the resistive path 23 to ground is of lesser magnitude than that found in either of the corresponding resistors 13 or 24. Closing of any switch 16 or 17 completes the corresponding circuit path so that direct current from the source 11 may pass therethrough to ground, thus rendering the electronic switch 12 conductive, thereby enabling the audio-signal previously blocked by the electronic switch 12 to pass through the now closed switch 16 or 17 and to be coupled `by the corresponding coupling capacitor 20 and tab switch 21 to the converting means 22.

Disregarding the presence of the further source of D.C.voltage 24, which means can be omitted, it is apparent that when the various switches 16 and 17 are open, the potential of the source 11 will appear on one terminal of the electronic switch 12. The other terminal of the electronic switch thus merely floats, it being connected to the various open switches. To avoid any possibility that any electronic switch 12 willbe momentarily conductive due to some unforeseen transient condition, the further source of D.C.-voltage 24 may be included. A B+ voltage of substantially the same magnitude as appears on the source-connected terminal of each electronic switch 12 may thus be connected to the other terminal of each electronic switch 12 so that there is substantially no voltage drop thereacross, even when the electronic switch is nonconductive. Where a gas tube is used, an ignition potential of 70 volts will be typical. Thus, protection is provided against transient voltages up to at least 70. If one of the electronic switches 12 should thus become momentarily conductive, the worst that could occur would be momentary capacitative coupling across various switches 16, 17. However, since this is not likely to happen with the means 24 omitted, an extremely reliable circuit results when this feature is included.

, of the high impedance type.

The resistance or impedance to current flow of each of the resistors 24 is somewhat higher than that of the resistors 13 and 23. Thus, upon closing of a switch 16 or 17, negligible current iiows through the corresponding resistor 24 to ground, while the current How needed to ignite or otherwise render the electronic switch 12 conductive readily ows through the resistors 13 and 23. Thus, the various electronic switches 12 have a negligible Voltage drop thereacross, both when open and when conductive.

The switching means illustrated for the note C5 is provided in accordance with the present invention, While the switching means illustrated for the note C6 illustrates that heretofore known and used. For the note C6, the source 11 is connected through a coupling capacitor 30 to each of six parallel connected resistors 13, each of which is connected to a switch 17a, similar to the switch 17, except that each has been provided with a ground contact 31 and ground connection. The circuit provided for the note C5, either with or without the added B-lbias provided by the resistor 24, obtains the results of the somewhat more elaborate circuit illustrated for the note C6. However, it is to be noted that in place of six resistors 13, only one resistor 13 is used, that six ground contacts have been eliminated, and that the ground connections to the six ground contacts have been eliminated. Assuming that the same saving is accomplished for every note in an organ having a conventional sixty-note keyboard, it can be seen that use of this invention eliminates 300 resistors, eliminates 360 ground contacts for switches 17, eliminates 360 ground connections therefor, eliminates the labor of installing these many components, and eliminates the mechanical adjustment labor for each of the grounded contacts 31. In place of sixty capacitors 30, sixty electronic switches 12, which may be of the ordinary neon type, are employed. Even though this saving and simplification has been made, basic protection against unwanted capacitative coupling between switch elements has been preserved, even though the signal source is one It is to be understood that the A.C.signal or component from the source 11 may be of the sine wave type, square vwave type, or sawtooth wave type. Thus the exact nature of the wave form emanating from the voltage source 11 is not intended to be restricted.

Representative values for circuit components include the following:

Resistance 13 ohms 1,000,000 Resistance 23 do 100,000 Resistance 24 do 2,200,000 Resistance 26 do 200,000 Capacitor 20 mfd .02 Capacitor 30 mfd .01

Although various minor modifications might be suggested by those versedl in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such embodiments as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. An electrical circuit for a musical instrument, comprising in combination: a high impedance source of alternating signal Voltage having, Whenever energized, a D.C.- potential on such signal voltage; means for converting signal voltage into sound; a key-operated switch connected in series in a circuit path from said source to said converting means and adapted to be selectively closed; and a gas tube, having an ignition potenti-al below said D.C. potential, and connected in series in said path between said source and said key-operated switch.

2. An electrical circuit for a musical instrument, comprising in combination: a high impedance source of voltage having, when energized, both an A.C.-signal component and a D.C.-component at one terminal; a gas tube,

having an ignition potential below the potentials of said components, one terminal of said tube being connected to said source terminal; a key-operated switch having a terminal connected to the other side of said tube; an A.C.-responsive means, coupled to the other terminal of said key-operated switch, for converting the A.C.cornpo nent into sound; and a D.C.-conductive path to ground connected to said other terminal of said switch, said A.C.component being transmittable through said switch only when said tube is ignited by said D.C.component.

3. An electrical circuit for a musical instrument, comprising in combination: a high impedance source of signal voltage, including a resistor; means for converting signal voltage into sound; a plurality of parallel circuit paths from said source to said converting means, each of said paths including a key-operated switch connected in series in the corresponding path and adapted to be selectively closed; and an electronic switch having a minimum conducting potential below said voltage, said resistor and said electronic switch being common to and in series with all of said circuit paths, and being disposed in series between said source and said converting means through the corresponding key-operated switch.

4. An electrical circuit for a musical instrument, comprising in combination: a high impedance source of signal voltage, including a resistor; means for converting signal voltage into sound; a plurality of parallel circuit paths from said source to said converting means, each of said paths including in series a key-operated switch, connected to a common collector means, for selectively closing the corresponding path; and an electronic switch having a minimum conducting potential below said voltage, said resistor and said electronic switch being common to all of said circuit paths, and being disposed in series between said source and the corresponding key-operated switch.

5v. An electrical circuit for a musical instrument, comprising in combination: a plurality of high impedance sources of signal voltage, each including a resistor; means for converting signal voltage into sound; a plurality of parallel circuit paths from each of said sources to said converting means, each of said paths including in series a key-Operated switch for selectively closing the corresponding path; a collector member joining all of said switches together and to said converting means and comprising a portion of each of said paths; and an electronic switch for each of said sources, said electronic switch having a minimum conducting-effecting potential below said voltage, said resistor and said electronic switch of each of said sources being common to all of the circuit paths thereof and being disposed in series between the corresponding source and key-operated switch.

6. An electrical circuit for a musical instrument, comprising in combination: a high impedance source having a terminal constructed to provide an alternating signal voltage and a D.C.voltage; a gas tube, having an ignition potential below said voltages, one terminal of said tube being connected to said source terminal; a key-operated switch having a terminal connected to the other terminal of said tube, for selectively closing a circuit path from said source; means coupled to the other terminal of said key-operated switch for converting signal voltage into sound; and a second source of D.C.voltage connected to said other terminal of said tube, said second source having a polarity and magnitude similar to said D.C.voltage of said high impedance source.

7. An electrical circuit for a musical instrument, comprising in combination: a high impedance source having a terminal constructed to provide an alternating signal voltage and a D.C.voltage; a gas tube, having an ignition potential below said voltages, one terminal of said tube being connected to Said source terminal; a key-operated switch having a terminal connected to the other terminal of said tube, for selectively closing a circuit path from said source; alternating signal-voltage responsive means coupled to the other terminal of said key-operated switch for converting signal voltage into sound; a second source of D.C.Voltage connected to said other terminal of said tube, said second source having a polarity and magnitude similar to said D.C.voltage of said high impedance source; and a D.C.conductive path to ground connected to said other terminal of said switch and having an impedance somewhat lower than that of said second source, said A.C.-voltage being transmittable through said keyoperated switch only when said tube is ignited by the D.C.-voltage, and said tube having negligible voltage drop thereacross during operation of the instrument when said key-operated switch is open.

8. An electrical circuit lfor a musical instrument, cornprising in combination: a high impedance source of alternating signal Voltage and a D.C.voltage, including a rst resistor; alternating signal-voltage responsive means -f-or converting signal voltage int-o sound; a plurality of parallel circuit paths from said source to said converting means, each of said paths including a key-operated switch for Kselectively closing the corresponding path; an electronic switch having a minimum conducting potential below said voltages; said iirst resistor and said electron-ic switch being common to all of said circuit paths, and being disposed in series between said source and the corresponding key-operated switch; a sec-ond resistor connected between said electronic switch on the terminal thereof mo-re `remote from -said source and a point in the circuit provid-ing a D.C.-voltage ot a polarity and magnitude equivalent to that of said source; and a resistive path 'to ground having a somewhat lower resistance than said second resistor, connected to said circuit between said key-operated switch and said converting means.

9. An electrical circuit for a musical instrument, comprising in combination: a plural-ity ot high impedance sources of combined alternating signal voltage and D C.- voltage, each source including a rst resistor; alternating signal-voltage responsive means for convertingl signal voltage into sound; a plurality of parallel circuit paths from each of said sources to said converting means, each of said paths including a key-operated switch for selectively cl-osing the corresponding path; a collector member joining all of said switches together and to said converting means and comprising a portion of each of said paths; an electronic switch `for each of said sources, said electronic switch having a minimum conducting potential below said combined voltages; said rst resistor and said electronic switch of each of said sources being common to all of the circuit paths thereof, and being disposed in series between said sou-rce and the corresponding keyopera-ted switch; a second resistor for each of said sources, each said resistor being connected between said electronic switch on the terminal thereof more remote from said source land a point in the circuit providing a D.C.voltage lof -a polarity and magnitude equivalent to that of said source; and a resistive path to ground having a somewhat lower resist-ance than said second resistor, connected to said collector member.

References Cited by the Examiner UNITED STATES PATENTS 2,486,208 10/ 1949 Rienstra Slt-1.26 2,811,887 11/1957 Anderson et al. S11-1.01

JOHN W. HUCKERT, Primary Examiner.

CARL W. ROBINSON, ARTHUR GAUSS, Examiners. 

1. AN ELECTRICAL CIRCUIT FOR A MUSICAL INSTRUMENT COMPRISING IN COMBINATION: A HIGH IMPEDANCE SOURCE OF ALTERNATING SIGNAL VOLTAGE HAVING, WHENEVER ENERGIZED, A D.C.POTENTIAL ON SUCH SIGNAL VOLTAGE; MEANS FOR CONVERTING SIGNAL VOLTAGE INTO SOUND; A KEY-OPERATED SWITCH CONNECTED IN SERIES IN A CIRCUIT PATH FROM SAID SOURCE TO SAID CONVERTING MEANS AND ADAPTED TO BE SELECTIVELY CLOSED; AND A GAS TUBE, HAVING AN IGNITION POTENTIAL BELOW SAID D.C.POTENTIAL, AND CONNECTED IN SERIES IN SAID PATH BETWEEN SAID SOURCE AND SAID KEY-OPERATED SWITCH. 